The German Patent Specification No. 256653, published in 1912, describes a method of drying solid bodies in which the bodies are immersed in a liquid heated to a temperature in excess of 100.degree. C.
The Swedish Patent Specification No. 321 195, published in 1970 describes a method for drying metal oxides in which the metal oxide is immersed in finely-divided form into a liquid hydrocarbon which is heavier than water, thereby to displace the water from the oxide. This specification recommends that the mixture is heated to a temperature of approximately 100.degree. C.
In a method described in U.S. Pat. No. 2,236,445, coal is dried by immersing the coal in a hot liquid.
These specifications clearly show that the technique of drying material by displacing water therefrom with the aid of a liquid is well known. It is, of course, also known to remove water from a material by heating the material.
Finally, it is also known to remove water and moisture from materials, by exposing the materials to a pressure beneath ambient or atmospheric pressure; for example many vacuum-drying methods are known to the art.
All known drying methods, however, require energy or are expensive to carry out, and there is a great need for drying methods and dewatering methods by means of which moist bituminous and lignocellulosic materials can be dried to form suitable fuels at a cost which is sufficiently low for these materials to compete with oil and high-grade coal. Before the price of oil began to rise at the beginning of the 1970's, there was very little interest in using alternative energy sources. The price of oil can hardly be expedted to fall in the future. Because of this, efforts are being made to find other energy sources, and particularly other fuels capable of replacing oil. Deposits of high-grade coal are limited and consequently efforts have been made to utilize low-grade carbonaceous fuels, such as peat, brown coal and forest waste. The water contained by these materials constitutes a problem when using the same as fuels.
Consequently there is a great need for new de-watering methods in the producton of fuels, in which methods the criterion of low energy costs is of the highest importance.